Fitness Gains Fail to Shield Leg Arteries From Prolonged Sitting, Dalhousie Trial Shows

The Dalhousie study (n=21 healthy young adults; 11 assigned to 12-week HIIT, 10 controls) used ultrasound to track popliteal artery flow-mediated dilation before and after two hours of uninterrupted sitting. Aerobic capacity rose in the exercise arm, yet sitting-induced impairment remained statistically identical to baseline and to the control group. This non-randomized, unblinded design with a narrow demographic limits causal claims and external validity; conflicts of interest were not disclosed. Earlier work by Thosar et al. (2014, Medicine & Science in Sports & Exercise, n=12) similarly isolated acute sitting effects on lower-limb vasodilation independent of fitness, while a 2022 systematic review in the British Journal of Sports Medicine (35 studies, mixed designs) concluded that only interrupting bouts of sitting, not total exercise volume, reliably preserves endothelial function. The Dalhousie findings therefore extend rather than contradict the pattern: cardiorespiratory improvements do not neutralize the immediate vascular consequences of immobility, urging workplace policies that prioritize movement breaks over sole reliance on after-work training.